Methods and apparatus for passive detection of objects in shallow waterways

Abstract

A method and system for detecting watercraft in shallow waterways. In one example, an underwater detection system includes an underwater power source, an acoustic sensor, a controller coupled to the power source and to the acoustic sensor and configured to detect a watercraft of interest based on acoustic signals generated by the watercraft of interest and received by the acoustic sensor, and a retractable communications system. The retractable communications system is configured to deploy a transmitter to the surface of the shallow water to report detection of a watercraft in the waterway and to retract the transmitter to a safe depth below the surface of the shallow waterway when not actively communicating.

What is claimed is: 
     
         1 . An underwater detection system comprising:
 an underwater power source;   an acoustic sensor configured detect underwater acoustic signals and to provide corresponding electrical signals;   a controller coupled to the power source and to the acoustic sensor and configured to receive and process the electrical signals, to determine whether the acoustic signals were generated by a watercraft of interest, and to produce a warning signal responsive to determining that at least one acoustic signal was generated by the watercraft of interest; and   a retractable communications system coupled to the controller and the power source and including a communications buoy configured to deploy to a water surface to transmit the warning signal and to be retracted below the water surface.   
     
     
         2 . The underwater detection system of  claim 1 , wherein the acoustic sensor includes a hydrophone. 
     
     
         3 . The underwater detection system of  claim 1 , wherein the retractable communications system includes a cable coupled to the communications buoy and a cable payout system coupled to the controller, the controller being configured to control the cable payout system to deploy the communications buoy to the water surface and to retract the communications buoy below the water surface. 
     
     
         4 . The underwater detection system of  claim 3 , wherein the communications buoy includes a wireless transmitter configured to transmit the warning signal. 
     
     
         5 . The underwater detection system of  claim 4 , wherein the warning signal includes information identifying at least one of the watercraft of interest, the underwater detection system, and a geographical position of the underwater detection system. 
     
     
         6 . The underwater detection system of  claim 4 , wherein the communications buoy further includes a wireless receiver configured to receive control signals from a remote control station. 
     
     
         7 . The underwater detection system of  claim 1 , wherein the underwater power supply includes a fuel cell. 
     
     
         8 . The underwater detection system of  claim 1 , wherein the underwater power supply includes a battery. 
     
     
         9 . The underwater detection system of  claim 8 , wherein the communications buoy is further configured to transmit a low-battery status signal. 
     
     
         10 . A method of detecting watercraft in a shallow waterway using an underwater detection system, the method comprising:
 detecting underwater acoustic signals;   processing the acoustic signals underwater to determine whether at least one of the acoustic signals was generated by a watercraft of interest;   producing a warning signal responsive to determining that the at least one acoustic signal was generated by the watercraft of interest;   deploying a communications buoy to a water surface of the shallow waterway;   transmitting the warning signal from the communications buoy; and   retracting the communications buoy to below the water surface after transmission of the warning signal is complete.   
     
     
         11 . The method of  claim 10 , wherein deploying the communications buoy includes paying out a cable coupled to the communications buoy to deploy the communications buoy to the water surface. 
     
     
         12 . The method of  claim 10 , wherein processing the acoustic signals includes analyzing a sound profile of the watercraft of interest. 
     
     
         13 . The method of  claim 10 , wherein producing the warning signal includes producing the warning signal including information identifying at least one of the watercraft of interest, the underwater detection system, and a geographical position of the underwater detection system. 
     
     
         14 . The method of  claim 10 , further comprising transmitting from the communications buoy information identifying a power status of the underwater detection system. 
     
     
         15 . The method of  claim 10 , wherein transmitting the warning signal includes transmitting the warning signal using a secure communications channel. 
     
     
         16 . The method of  claim 10 , further comprising receiving a control signal for the underwater detection system. 
     
     
         17 . The method of  claim 16 , wherein receiving the control signal includes receiving the control signal at the communications buoy while the communications buoy is at the water surface. 
     
     
         18 . The method of  claim 16 , wherein receiving the control signal includes receiving a retrieval signal, and further comprising:
 deploying the communications buoy to the water surface responsive to receiving the retrieval signal.   
     
     
         19 . The method of  claim 10 , wherein retracting the communications buoy includes retracting the communications buoy to a predetermined depth below the water surface, the predetermined depth being below a maximum draft depth of watercraft expected in the shallow waterway. 
     
     
         20 . An underwater watercraft detection system configured to be deployed in a shallow waterway and comprising:
 an underwater power source;   an acoustic sensor;   a controller coupled to the power source and to the acoustic sensor and configured to detect a watercraft of interest based on acoustic signals generated by the watercraft of interest and received by the acoustic sensor;   a retractable communications buoy coupled to the controller; and   a cable system including a cable coupled to the communications buoy and a cable payout system coupled to the power source and the controller;   wherein the controller is configured to control the cable payout system to deploy the communications buoy to a surface of the shallow waterway, to control the communications buoy to transmit a warning signal responsive to detection of the watercraft of interest, and to control the cable payout system to retract the communications buoy to a predetermined depth below the surface of the shallow waterway subsequent to completion of transmission of the warning signal.